Les Mikesell wrote:
Robert Nichols wrote:
These shouldn't make any difference. The limit is on the size of the expanded shell command line.
Really?
$ M=0; N=0; for W in `find /usr -xdev 2>/dev/null`; do M=$(($M+1)); N=$(($N+${#W}+1)); done; echo $M $N 156304 7677373
vs.
$ /bin/echo `find /usr -xdev 2>/dev/null` bash: /bin/echo: Argument list too long
For the first case, the shell never tries to pass the list as command arguments. It builds the list internally, limited only by memory size, and processes the words one by one.
Is that peculiar to bash? I thought the `command` construct was expanded by shells into the command line before being evaluated.
I can't answer for how any particular shell allocates its internal memory, but yes, the shell does read the entire output from `command` before evaluating it. If this data is simply being used internally it never gets passed to the kernel as an argument to exec() and thus can never result in errno==E2BIG (7, "Argument list too long").